% add the PATH to retrieve cls and sty beamer styles files \makeatletter \providecommand*{\input@path}{} \edef\input@path{{../../support/beamer/}\input@path}% prepend \makeatother % \documentclass{pharoslides} % \documentclass[aspectratio=169]{pharoslides} % format 16/9 \documentclass[withvideo]{pharoslides} % format 16/9 + incrustation video \graphicspath{{./figures/}{../}{../../support/beamer/imgs/}} %Information to be included in the title page: \title{Understanding Metaclasses} \subtitle{} \author{Damien Cassou, Stéphane Ducasse and Luc Fabresse} \institute{http://stephane.ducasse.free.fr} \date{} \slidesid{W7S03} \begin{document} \frame[plain]{\titlepage} \begin{frame}[fragile] \frametitle{What You Will Learn} \begin{itemize} \item Not needed to program in Pharo :) \item But intellectually exciting \begin{itemize} \item Where \code{new} is defined? \item What is the class of a metaclass? \item Uniformity of the instance relationship \end{itemize} \end{itemize} \end{frame} \begin{frame}[fragile] \frametitle{The Key: Only One Method Lookup} \begin{columns} \begin{column}{0.6\textwidth} When a message is sent to an object, a method is searched starting from the class of the object and following the inheritance chain \end{column} \begin{column}{0.4\textwidth} \begin{center} \includegraphics[width=1.5\textwidth]{figures/LookupEssenceWithGeneric.png}\end{center} \end{column} \end{columns} \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item Every class eventually inherits from \code{Object} \item Every class is an instance of a metaclass \item The metaclass hierarchy parallels the class hierarchy \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item Every metaclass is an instance of \code{Metaclass} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item \textbf{Every object is an instance of a class} \item Every class eventually inherits from \code{Object} \item Every class is an instance of a metaclass \item The metaclass hierarchy parallels the class hierarchy \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item Every metaclass is an instance of \code{Metaclass} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Every Object is an Instance of a Class} \begin{center} \includegraphics[width=0.6\textwidth]{figures/01-SortedCollectionInstanceOfSortedCollection.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item \textbf{Every class eventually inherits from \code{Object}} \item Every class is an instance of a metaclass \item The metaclass hierarchy parallels the class hierarchy \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item Every metaclass is an instance of \code{Metaclass} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Every Class Eventually Inherits From Object} \begin{center} \includegraphics[width=0.7\textwidth]{figures/02-SortedCollectionInheritsFromObject.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Responsibility of Object} Class \code{Object} represents the common object behavior \begin{itemize} \item error handling, halting, announcements \item all classes eventually inherit from \code{Object} \end{itemize} \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item Every class eventually inherits from \code{Object} \item \textbf{Every class is an instance of a metaclass} \item The metaclass hierarchy parallels the class hierarchy \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item Every metaclass is an instance of \code{Metaclass} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Every class is an instance of a metaclass} Classes are objects too! \begin{itemize} \item Every class \code{X} is the unique instance of its metaclass, called \code{X class} \end{itemize} \begin{center} \includegraphics[width=1.1\textwidth]{figures/04-OrderedCollectionIsInstanceOfOrderedCollectionClass.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Metaclass are Implicit} Metaclasses are automatically created when creating a class \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item Every class eventually inherits from \code{Object} \item Every class is an instance of a metaclass \item \textbf{The metaclass hierarchy parallels the class hierarchy} \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item Every metaclass is an instance of \code{Metaclass} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Metaclass Hierarchy Parallels Class Hierarchy} \begin{center} \includegraphics[width=1.2\textwidth]{figures/05-OrderedCollectionIsInstanceOfOrderedCollectionClassInherit}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Sending a Message to a Class} \begin{center} \includegraphics[width=1.4\textwidth]{figures/06-OrderedCollectionIsInstanceOfOrderedCollectionClass}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Questions} \begin{itemize} \item What is the class of a metaclass? \item What is the superclass of \code{Object class}? \item What about sending a message to a metaclass? \end{itemize} \begin{center} \includegraphics[width=1.1\textwidth]{figures/07-2Questions.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item Every class eventually inherits from \code{Object} \item Every class is an instance of a metaclass \item The metaclass hierarchy parallels the class hierarchy \item \textbf{Every metaclass inherits from \code{Class} up to \code{Behavior}} \item Every metaclass is an instance of \code{Metaclass} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Every Metaclass Inherits from Class up to Behavior} \begin{center} \includegraphics[width=1.0\textwidth]{figures/08-BehaviorClassDescriptionAndClass.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Where new is Defined?} \begin{center} \includegraphics[width=1.0\textwidth]{figures/09-BehaviorClassDescriptionAndClassWithNew.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Responsibilities of Behavior} \code{Behavior} \begin{itemize} \item Minimum state for objects that \textbf{have instances} \item State: \begin{itemize} \item superclass link, method dictionary, description of instances (representation and number) \end{itemize} \item Methods: \begin{itemize} \item method dictionary, compiling method \item instance creation (\code{new}, \code{basicNew}, \code{new:}, \code{basicNew:}) \item class hierarchy manipulation (\code{superclass:}, \code{addSubclass:}) \item accessing (\code{selectors}, \code{allSelectors}, \code{compiledMethodAt:}, \code{allInstances}, \code{instVarNames}) \end{itemize} \end{itemize} \end{frame} \begin{frame}[fragile] \frametitle{Responsibilities of ClassDescription} \code{ClassDescription} \begin{itemize} \item Abstract class superclass of \code{Class} and \code{Metaclass} \item Adds a number of facilities to \code{Behavior}: \begin{itemize} \item named instance variables \item category organization for methods \item the notion of a name (abstract) \item maintenance of Change sets and logging changes \item most of the mechanisms needed for fileOut \end{itemize} \end{itemize} \end{frame} \begin{frame}[fragile] \frametitle{Responsibilities of Class} \code{Class} \begin{itemize} \item represents the common behavior of all classes \begin{itemize} \item name, compilation, method storing, instance variables ... \end{itemize} \item representation for classVariable names (\code{addClassVarName:}, \code{initialize}) \end{itemize} \end{frame} \begin{frame}[fragile] \frametitle{Classes are Instances of Metaclasses} Metaclass and class inheritances are parallel \begin{center} \includegraphics[width=1.0\textwidth]{figures/10-BehaviorClassDescriptionAndClassWithMetaclasses.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item Every class eventually inherits from \code{Object} \item Every class is an instance of a metaclass \item The metaclass hierarchy parallels the class hierarchy \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item \textbf{Every metaclass is an instance of \code{Metaclass}} \item The metaclass of \code{Metaclass} is an instance of \code{Metaclass} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{Every Metaclass is an Instance of Metaclass} \code{Metaclass} inherits from \code{ClassDescription} \begin{center} \includegraphics[width=1.15\textwidth]{figures/11-BehaviorClassDescriptionAndClassWithMetaclassesInstanceOfMetaclass.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Metaclass Responsibilities} \code{Metaclass} is responsible for creating and initializing a metaclass's sole instance (a Class) \end{frame} \begin{frame}[fragile] \frametitle{Metaclasses in 7 Points} \begin{enumerate} \item Every object is an instance of a class \item Every class eventually inherits from \code{Object} \item Every class is an instance of a metaclass \item The metaclass hierarchy parallels the class hierarchy \item Every metaclass inherits from \code{Class} up to \code{Behavior} \item Every metaclass is an instance of \code{Metaclass} \item \textbf{The metaclass of \code{Metaclass} is an instance of \code{Metaclass}} \end{enumerate} \end{frame} \begin{frame}[fragile] \frametitle{The metaclass of Metaclass is an Instance of Metaclass} \begin{center} \includegraphics[width=1.3\textwidth]{figures/12-FullMetaclasses.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{Observations} \begin{columns} \begin{column}{0.7\textwidth} \begin{itemize} \item When programming we do not really care about that! \item Now the full graph is consistent \begin{itemize} \item Any class can receive a message \item Only one message lookup \end{itemize} \end{itemize} \end{column} \begin{column}{0.3\textwidth} \begin{center} \includegraphics[width=1.8\textwidth]{figures/LookupEssenceWithGeneric.png}\end{center} \end{column} \end{columns} \end{frame} \begin{frame}[fragile] \frametitle{A Consistent World} \begin{center} \includegraphics[width=1.3\textwidth]{figures/12-FullMetaclasses.png}\end{center} \end{frame} \begin{frame}[fragile] \frametitle{What You Should Know} \begin{itemize} \item Classes are objects and can receive messages \item The process is \textbf{exactly} the same as for any other objects \end{itemize} \end{frame} % \setlength{\textwidth}{\originaltextwidth} \setbeamertemplate{background canvas}{\insertBorderForHandout} \begin{frame}[plain] \begin{minipage}{\originaltextwidth} \centering \large \vspace{2em} A course by \vspace{1em} \hspace{-20px}\includegraphics[height=32px]{inriaLogo}\hspace{3em}\raisebox{7px}{and}\hspace{3em}\raisebox{-6px}{\includegraphics[height=30px]{logoutop}} \vspace{2em} in collaboration with \vspace{1em} \includegraphics[height=40px]{unisciellogo}\hskip 1.5em% \raisebox{5px}{\includegraphics[height=30px]{unitlogo}}\hskip 2em% \raisebox{8px}{\includegraphics[height=24px]{univLilleLogo}}\hskip 2em% \raisebox{3px}{\includegraphics[height=29px]{logo-IMT}}\hskip 2em% \raisebox{1px}{\includegraphics[height=32px]{minesDouaiLogo}} \vspace{2.5em} \includegraphics[width=50px]{by-nc-nd} \tiny \hskip 0.5em \raisebox{5px}{Inria 2016} \medskip \tiny Except where otherwise noted, this work is licensed under CC BY-NC-ND 3.0 France \url{https://creativecommons.org/licenses/by-nc-nd/3.0/fr/} \end{minipage} \end{frame} \end{document} %%% Local Variables: %%% mode: latex %%% TeX-master: t %%% End: